In a typical inkjet recording or printing system, ink droplets are ejected from a nozzle at high speed towards a recording element or medium to produce an image on the medium. The ink droplets, or recording liquid, generally comprise a recording agent, such as a dye or pigment, and a large amount of solvent. The solvent, or carrier liquid, typically is made up of water, an organic material such as a monohydric alcohol, a polyhydric alcohol, or mixtures thereof.
An inkjet recording element typically comprises a support having on at least one surface thereof at least one ink-receiving layerink-receiving layer. The ink-receiving layer is typically either a porous layer that imbibes the ink via capillary action, or a polymer layer that swells to absorb the ink. Swellable hydrophilic polymer layers take an undesirably long time to dry compared to porous ink-receiving layers.
Porous ink-receiving layers are usually composed of inorganic or organic particles bonded together by a binder. The amount of particles in this type of coating is often far above the critical particle volume concentration (CPVC), which results in high porosity in the coating. During the inkjet printing process, ink droplets are rapidly absorbed into the coating through capillary action and the image is dry-to-touch right after it comes out of the printer.
Inkjet prints, prepared by printing onto inkjet recording elements, are subject to environmental degradation. They are especially vulnerable to damage resulting from contact with water and atmospheric gases such as ozone. Ozone bleaches inkjet dyes resulting in loss of density. The damage resulting from the post imaging contact with water can take the form of water spots resulting from deglossing of the top coat, dye smearing due to unwanted dye diffusion, and even gross dissolution of the image recording layer. To overcome these deficiencies, inkjet prints are often laminated. However, lamination is expensive, as a film laminate is a separate roll of material which -requires an adhesive layer prepared via an additional coating step. If the laminate is of the transfer type there is also added waste in the form of the exhausted coated support from which the laminate is transferred. Accordingly, efforts have been made to provide, in the form of a single sheet, an image-recording medium that has an uppermost fusible porous layer which functions as a latent protective layer. This layer generally comprises fusible thermoplastic particles. It is often characterized as an ink-transporting layer when it is not retentive of the ink or colorant, which passes through to an underlying layer. When the layer functions as an ink-transporting layer, fusing transforms it into a protective topcoat for the underlying image. This single-sheet media design thereby eliminates the need for lamination to protect inkjet prints.
There remain problems with this approach, however, in terms of choosing the appropriate thermoplastic material with which to form the fusible particles of the uppermost layer. Specifically, it is difficult to simultaneously meet the requirements of: fusibility, and then subsequent to fusing flexibility, and resistance to thermal blocking in the fused layer.
U.S. Pat. Nos. 4,785,313 and 4,832,984 relate to an inkjet recording element comprising a support having thereon a fusible, ink-transporting layer and an ink-retaining layer, wherein the ink-retaining layer is non-porous. However, there is a problem with this element in that fused prints crack when bent and they exhibit thermally blocking.
EP 858,905A1 relates to an inkjet recording element having a porous, outermost layer formed by heat sintering thermoplastic particles of latex such as polyurethane which may contain a slight amount of a hydrophilic binder such as poly(vinyl alcohol). However, there is a problem with this element in that it has poor resistance to mechanical abrasion, when it does not contain a hydrophilic binder, and poor water-resistance when it does contain a hydrophilic binder.
U.S. Pat. No. 6,087,051 relates to an information recording material having a support and an image carrier layer and an outermost protective covering layer on the image carrier layer, wherein the protective covering layer contains an aqueous polyurethane resin which comprises a polycarbonate ester. There is a problem with this element in that it exhibits thermal blocking.
U.S. Pat. No. 6,866,384 discloses particles of segmented and non-segmented polyurethane in fusible layer of inkjet media compared to particles made from cellulose acetate butyrate. The latter was found to provide superior thermal blocking and print cracking. However, the process to produce fusible particles made from cellulose acetate butyrate requires large amounts of organic solvents such as ethyl acetate.
It is an object of this invention to provide a porous uppermost layer that has good mechanical integrity and is abrasion resistant. It is another object of the invention to provide an uppermost layer that is thermally fusible and thereby can be transformed by fusing into a protective layer. It is desirable that the thermally fusible material can be prepared in and coated from an aqueous system. It is another object of the invention to provide an inkjet recording element wherein the uppermost layer is sufficiently flexible after fusing that it can be bent without excessive cracking. It is another object to provide an inkjet recording element wherein the fused uppermost layer doesn't exhibit thermal blocking. Achieving such a balance of properties is a significant challenge.